"use strict";

var canvas = document.getElementById('canvas'),
	ctx = canvas.getContext('2d'),
	w = canvas.width = window.innerWidth,
	h = canvas.height = window.innerHeight,

	hue = 217,
	stars = [],
	count = 0,
	maxStars = 1200;

var canvas2 = document.createElement('canvas'),
	ctx2 = canvas2.getContext('2d');
canvas2.width = 100;
canvas2.height = 100;
var half = canvas2.width / 2,
	gradient2 = ctx2.createRadialGradient(half, half, 0, half, half, half);
gradient2.addColorStop(0.025, '#fff');
gradient2.addColorStop(0.1, 'hsl(' + hue + ', 61%, 33%)');
gradient2.addColorStop(0.25, 'hsl(' + hue + ', 64%, 6%)');
gradient2.addColorStop(1, 'transparent');

ctx2.fillStyle = gradient2;
ctx2.beginPath();
ctx2.arc(half, half, half, 0, Math.PI * 2);
ctx2.fill();

// End cache

function random(min, max) {
	if (arguments.length < 2) {
		max = min;
		min = 0;
	}

	if (min > max) {
		var hold = max;
		max = min;
		min = hold;
	}

	return Math.floor(Math.random() * (max - min + 1)) + min;
}

function maxOrbit(x, y) {
	var max = Math.max(x, y),
		diameter = Math.round(Math.sqrt(max * max + max * max));
	return diameter / 2;
}

var Star = function() {

		this.orbitRadius = random(maxOrbit(w, h));
		this.radius = random(60, this.orbitRadius) / 12;
		this.orbitX = w / 2;
		this.orbitY = h / 2;
		this.timePassed = random(0, maxStars);
		this.speed = random(this.orbitRadius) / 900000;
		this.alpha = random(2, 10) / 10;

		count++;
		stars[count] = this;
	}

Star.prototype.draw = function() {
	var x = Math.sin(this.timePassed) * this.orbitRadius + this.orbitX,
		y = Math.cos(this.timePassed) * this.orbitRadius + this.orbitY,
		twinkle = random(10);

	if (twinkle === 1 && this.alpha > 0) {
		this.alpha -= 0.05;
	} else if (twinkle === 2 && this.alpha < 1) {
		this.alpha += 0.05;
	}

	ctx.globalAlpha = this.alpha;
	ctx.drawImage(canvas2, x - this.radius / 2, y - this.radius / 2, this.radius, this.radius);
	this.timePassed += this.speed;
}

for (var i = 0; i < maxStars; i++) {
	new Star();
}

function animation() {
	ctx.globalCompositeOperation = 'source-over';
	ctx.globalAlpha = 0.8;
	ctx.fillStyle = 'hsla(' + hue + ', 64%, 6%, 1)';
	ctx.fillRect(0, 0, w, h)

	ctx.globalCompositeOperation = 'lighter';
	for (var i = 1, l = stars.length; i < l; i++) {
		stars[i].draw();
	};

	window.requestAnimationFrame(animation);
}

animation();